Cholesterol feeding is commonly used for the induction of experimental atherosclerosis. It has been recently observed, however, that cholesterol is quite unstable and easily auto-oxidized when stored in air at room temperature. There is evidence to suggest that hypercholesterolemia may lead to arterial injury prior to deposition of lipid in the arterial wall. The mechanism and nature of this arterial injury are poorly characterized. It is our hypothesis that such injury may be induced by cholesterol oxidation products. We previously demonstrated that a concentrate of oxidation products prepared from aged cholesterol produced necrosis of rabbit aortic smooth muscle cells both in vitro and in vivo and that craters formed on the aortic luminal surface in vivo within a short period of time, whereas purified cholesterol showed no harmful effects. The exact mechanisms of cytotoxicity of cholesterol oxidation products are not fully understood, but they may possibly competitively replace some of cholesterol in the cell membrane and/or inhibit cholesterol biosynthesis, thereby resulting in cell death as a consequence of membrane dystufction. Further studies of these products on cell membranes, including their effects on membrane bound enzymes, membrane transport, endocytosis and IDL lipoprotein receptors, are therefore of great importance and will be done during this project. With regard to atherogenicity, it is essential ot demonstrate th at the suggested agents are being absorbed and transported in the blood to the arteries. Our proposed experiments using radioactive cholesterol oxidation products to trace their absorption, transport and tissue distribution will provide this data. Since the initial atherogenic events following arterial injury probably involve platelets and their release factors, the effects of cholesterol oxidation products on platelet adhesion, aggregation and endothelial prostacyclin synthesis will also be tested. Aditionally, we will assess the morphologic and biochemical effects of long-term feeding of small quantities of cholesterol oxidation products on the arteries of experimental animals. This data will be correlated with plasma lipid and lipoprotein patterns and with plasma and tissue concentrations of individual oxidation produced. By combining both morphologic and biochemical studies in vitro and in vivo experimental models, we will derive a comprehensive view of the role and mechanisms of cholesterol products in atherosclerosis.